This research is designed to understand factors leading to the reacquisition of sensitivity of the regenerating levator ani muscle in rats to testosterone. A major object is to learn whether this is a strictly hormonal process or whether it might also involve interactions between the regenerating muscle and nerves or other local factors. Another goal is to learn when the regenerating and embryonic levator ani muscles become sensitive to testosterone. This research will involve studies on the regeneration of the levator ani muscle in situ in heterotopic sites after complete crushing or free grafting. Regenerations will be studied in normal, in castrated and in testosterone treated rats. Means of analysis will be gross weight, histology, quantitative morphology, histochemistry, autoradiography, biochemistry and contractile analysis.